But for those with an irregular heartbeat — a common condition known as atrial fibrillation — it was even more effective.

Those people saw their chance of getting any cancer slashed by 38 per cent and of getting lung cancers by 61 per cent.

Prof James Lorens, of Norway’s Bergen University, said: “Our main finding is that a drug that has been in clinical use for more than 50 years and used by millions of adults worldwide, may protect against cancer.”

Nearly 11million prescriptions for warfarin were dispensed by the NHS last year. The blood-thinning drug costs as little as 63p for a month’s supply.